1. Field of the Invention
The invention relates to a structure for connecting neutral conductors in a stator winding of a three-phase motor.
2. Description of Related Art
An example of a conventional structure for connecting neutral conductors in a stator winding of a three-phase motor is shown in FIGS. 1 and 2. Neutral terminal portions 1a of coil conductors 1 in a stator winding of a three-phase motor are connected to each other at points 1b as shown in FIG. 1. The neutral terminal portions are connected to each other by means of a mechanical connection such as lapping and crimping, soldering, brazing, welding and the like. The thus connected neutral terminal portions and the mechanically connected neutral points 1b are disposed, as shown in FIGS. 1 and 2, juxtaposed at one end of the coil assembly 5 extending from the stator core 3 in the direction of the axial center of the stator 2 (i.e. the lateral direction in FIG. 2). This positioning of the connected neutral terminal portions 1a and mechanical connections 1b at the end of the coil assembly increases the axial length of the motor in the lateral direction in FIG. 2.
When the number of the coils wound in parallel is increased as in a motor for an electric vehicle, the larger the bundle of neutral conductors and neutral points at which the neutral conductors are connected, resulting in significant increase in the axial length of the motor. Since the space allowed for mounting a motor to an electric vehicle or the like is limited, it is desired that the axial length of the motor be as short as possible.
In view of the above, it is an object of the present invention to provide a three-phase motor enabling connection of neutral conductors without increasing the axial length of the motor.
To achieve the above construction, according to the invention, a structure is provided for connecting neutral conductors in a three-phase motor containing a stator core in which a coil assembly including three-phase coils is disposed and the neutral end portions of conductors of each coil are connected to each other so as to form neutral points. The three-phase motor is structured such that the neutral end portions of the conductors of the respective coils pass from the inside toward the outer periphery side of the coil assembly one by one where the neutral end portions are connected to a bus bar formed of a conductive material provided on the outside of the coil assembly. Therefore, bundle of connections of the neutral conductors and the connecting points are no longer disposed adjacent in the direction of the axial center, thereby eliminating the increase in axial length of the motor due to the connected neutral end portions of the coil conductors.
According to a preferred embodiment of the invention, connecting portions are formed on the bus bar for connecting the neutral end portions of the coil. Based on this structure, the neutral end portions of the coil conductors can be connected to the bus bar efficiently since the conductors can be connected, one by one, to the bus bar connecting portions.
According to another preferred form of the invention, a plurality of terminal members are detachably provided on the bus bar, and the connecting portions at which the neutral end portions of the coil conductors are connected are formed on terminal end members connected to the bus bar. Based on this structure, a plurality of neutral end portions of the coil conductors can be connected to the bus bar easily by connecting the conductors via the terminal members.
According to a further preferred form of the invention, the connecting portions are formed with slits. Based on this structure, good workability is achieved since the neutral end portions of the coil conductors can be connected by merely inserting tips of the neutral end portions into the slits.
According to another further preferred form of the invention, the connecting portions are formed with holes. Based on this structure, good workability is achieved since the neutral conductors can be connected by merely inserting tips of the neutral end portions of the coil conductors into the holes.
According to still another further preferred form of the invention, steps are formed in the connecting portions, and an electrical connection is made between the connecting portions and the neutral end portions of the coil conductors by breaking or penetrating an insulative coating on the conductors utilizing contact pressure between the steps and the conductors. Based on this structure, a high efficiency of connection work is achieved since the coating of the neutral end portions of the coil conductors can be broken by utilizing the steps.
According to another preferred form of the invention, the steps are formed from a cross sectional portion of a plurality of laminated thin sheets. Based on this structure, the steps can be formed easily by laminating the thin sheets, which is convenient.
According to still another preferred form of the invention, the steps are formed with a hole into which the neutral end portions of the coil conductors are inserted and a leaf spring formed with the tip thereof facing the hole. Based on this structure, the coating can be broken by engagement with the tip of the leaf spring.
According to yet another preferred form of the invention, the bus bar is formed of a plate-shaped member formed in an arc along the outer periphery portion of the stator core. Based on this structure, the bus bar can be disposed utilizing a space in the outer periphery portion of the stator core.
According to yet still another preferred form of the invention, a plurality of bus bars are installed on the outer periphery portion of the stator core. Based on this structure, providing a plurality of bus bars allows a plurality of three-phase winding coils to be accommodated.
According to another preferred form of the invention, the neutral end portions of the coil conductors are aligned along a plane perpendicular to the axial direction of the stator core. Based on this structure, the space that the neutral end portions of the coil conductors occupy in the direction of the core axis direction is kept to a minimum, thereby preventing the axial length of the motor from becoming longer.
According to another preferred form of the invention, a plurality of neutral end portions of the coil conductors are crimped in an aligned form by means of crimping members and connected to the bus bar via the crimping members. Based on this structure, the neutral end portions of the coil conductors can be arranged in a line efficiently, thereby contributing to more efficient assembling.
According to another preferred form of the invention, the three-phase motor comprises includes terminal members at the tips of the neutral end portions of the coil conductors, and is structured such that the neutral end portions of the coil conductors are connected to the bus bar via the terminal members. Based on this structure, the neutral end portions of the coil conductors can be easily connected to the bus bar via the terminal members.
According to another preferred form of the invention, the width of the bus bar in the axial direction of the stator is formed smaller than the width of the coil assembly in the axial direction of the stator core. Based on this structure, the bus bar does not project from the coil assembly outward in the axial direction, preventing the axial length of the motor being extended due to neutral connection points.